[dm-devel] [PATCH V3] blk-mq: introduce BLK_STS_DEV_RESOURCE

[Bart Van Assche]

On Sat, 2018-01-27 at 19:23 -0500, Mike Snitzer wrote:
> On Sat, Jan 27 2018 at  5:12pm -0500,
> Bart Van Assche <Bart.VanAssche at wdc.com> wrote:
> > - The patch at the start of this thread introduces a regression in the
> >   SCSI core, namely a queue stall if a request completion occurs concurrently
> >   with the newly added BLK_MQ_S_SCHED_RESTART test in the blk-mq core.
> 
> And why is this supposed race unique to SCSI core?  

That race is not unique to the SCSI core. It is possible that the patch at
the start of this thread introduces the same race in other block drivers
but I have not yet tried to verify that.

> Fact is Ming dutifully implemented what Jens suggested.

That's a misleading statement. Jens proposed to introduce a new status code
(which he called "NO_DEV_RESOURCE") but did not specify any of the other
aspects of Ming's patch. Jens definitely did not ask to introduce new race
conditions. See also https://www.spinics.net/lists/kernel/msg2703154.html

Bart.